Algorithm Design

Algorithm: method for solving a problem. What is an algorithm? Algorithm: method for solving a problem. Data structure: method to store information.

Broad and far-reaching impact in the real world Why study an Algorithm? Broad and far-reaching impact in the real world Internet: Web search, packet routing, distributed file sharing, ... Biology: Human genome project, protein folding, … Computers: Circuit layout, file system, compilers, … Computer graphics: Movies, video games, virtual reality, … Security: Cell phones, e-commerce, voting machines, … Multimedia: MP3, JPG, DivX, HDTV, face recognition, … Social networks: Recommendations, news feeds, advertisements, … Physics: N-body simulation, particle collision simulation, …

Why study an Algorithm? For Intellectual Stimulation “ For me, great algorithms are the poetry of computation. Just like verse, they can be terse, allusive, dense, and even mysterious. But once unlocked, they cast a brilliant new light on some aspect of computing. ” — Francis Sullivan “ An algorithm must be seen to be believed. ” — Donald Knuth

Why study an Algorithm? For Intellectual Stimulation “ For me, great algorithms are the poetry of computation. Just like verse, they can be terse, allusive, dense, and even mysterious. But once unlocked, they cast a brilliant new light on some aspect of computing. ” — Francis Sullivan “ An algorithm must be seen to be believed. ” — Donald Knuth

Why study an Algorithm? To become a proficient programmer. “ I will, in fact, claim that the difference between a bad programmer and a good one is whether he considers his code or his data structures more important. Bad programmers worry about the code. Good programmers worry about data structures and their relationships. ” — Linus Torvalds (creator of Linux) “ Algorithms + Data Structures = Programs. ” — Niklaus Wirth

Characteristics of a good algorithm An algorithm is any well-defined computational procedure that takes some value, or set of values, as input and produces some value, or set of values, as output. An algorithm is thus a sequence of computational steps that transform the input into the output. Predict performance in terms of time and space complexities. – Number of steps, recursion and processing should be optimized.

Understand Problems & Build algorithms Learning Objectives Understand Problems & Build algorithms Analyse algorithm for following design requirements Functional Performance Reliability Modularity Extensibility Parallelism Portability

Component Design Software Component Output Formatting Input Validation Data Storage Core Algorithm Output Formatting Interface 1 Interface 2 Interface 3 Software Component

Component design – key aspects to consider What is the basic problem that this component is addressing? What are the inputs needed and their characteristics? Configurable parameters – data types, i/o interfaces, non-functional requirements Data that would be used for computing Interfaces – keyed in inputs, files, shared memory, message pipes, queues etc What are the input validations required? Remember – Garbage In-Garbage Out How is the input data and output data stored? – data structures What are the expected outputs and their characteristics? What are the non-functional requirements? Performance – load handling, latency, portability, security, reliability etc.

Module Design Output Interface Input Interface Platform Interface Input Validation Data Storage Core Algorithm Output Formatting Interface 1 Interface 2 Interface 3 Software Component Platform Interface Input Interface Output Interface Input buffers Output buffers

System Design – Layered Architecture Source: https://msdn.microsoft.com/en-us/library/ee658124.aspx

Module/Design Steps Decompose system/module into components and interfaces i.e., identify the software architecture Determine relationships between components e.g., identify component dependencies and determine inter-component communication mechanisms Specify component interfaces Interfaces should be well-defined - Facilitates component testing and team communication Describe component functionality - informally or formally Identify opportunities for systematic reuse - Both top-down and bottom-up

Typical Architecture Patterns Category Architectural Design Description Communication Message bus Prescribes use of a software system that can receive and send messages using one or more communication channels. Service–Oriented Architecture (SOA) Defines the applications that expose and consume functionality as a service using contracts and messages. Deployment Client/server Separate the system into two applications, where the client makes requests to the server. 3-tier or N-tier Separates the functionality into separate segments with each segment being a tier located on a physically separate computer. Domain Domain Driven Design Focused on modeling a business domain and defining business objects based on entities within the business domain. Structure Component Based Breakdown the application design into reusable functional or logical components that expose well-defined communication interfaces. Layered Divide the concerns of the application into stacked groups (layers). Object oriented Based on the division of responsibilities of an application or system into objects, each containing the data and the behavior relevant to the object.

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